A solid free drilling fluid with high temperature resistance

The formation temperature of carbonate reservoir with the depth of 4000 m may be more than 150 ℃, so the common solid free drilling fluid cannot meet the requirement. By comparing the ratio of yield point to plastic vicosity and temperature resistant limit, viscosifying agents VP and XC are selected. And the fluid loss additives are optimized through the thermal analysis and filtration experiments. Finally, a type of high temperature resistant solid free drilling fluid is formed, with the composition of 3%CMJ+2%RHJ+0.2%XC+0.3%VP+3%SMP-2+1%~ saturated NaCOOH. The test results show that the system can resist 200 ℃ and 20% drilling cuttings, and the calcium tolerance is 5% and salt tolerance is 20% or more. And the extreme pressure lubrication coefficient is 0.098 and permeability recovery value is above 90%, which can meet the requirements of drilling deep carbonate reservoir and demonstrate good deep fractured carbonate reservoir protection performance.